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## Windbreak Function (How do they work?)

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**Windbreak Function(How do they work?)**Joe Zeleznik NDSU Extension Forester**Windbreak Function - Basics**• They slow down the wind • They re-direct the wind • Which modifies the microclimate and environment in protected areas**Based on Structure**• Density - % solid**Based on Structure**• Density - % solid • Height – changes over time – height of tallest row**Based on Structure**• Density - % solid • Height – changes over time – height of tallest row • Length –**Based on Structure**• Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds**From Northerly or northwesterly Direction 12 out of 24**From Southeasterly or Easterly Direction 10 out of 24 From Southwesterly Direction 2 out of 24**Based on Structure**• Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds • Continuity**Based on Structure**• Density - % solid • Height – changes over time – height of tallest row • Length – • Orientation – perpendicular to prevailing winds • Continuity • Species/Number of Rows**Windspeed in the open**Fastest Slowest Ground**Windspeed in the open**Fastest Slowest No turbulence over smooth ground Ground Turbulent flow over a rough surface**Windspeed in the open**Fastest Turbulent - Random Slowest No turbulence over smooth ground Ground Turbulent flow over a rough surface Eddy – Circular, against main flow**Terms to know:**H = height of object Upwind Windward Downwind Leeward**Pressure eddy**Solid barrier 1-2H**Suction eddy**Turbulent wake zone Resumption of open-field flow Solid barrier 1-3H 3-6H 6-8H**Porous barrier**Lower effect of pressure eddy**Porous barrier**Resumption of open-field flow Lower effect of suction eddy Turbulent wake farther downwind**Lower branches pruned**Resumption of open-field flow Increased snow spreading? Even lower effect of suction eddy Turbulent wake even farther downwind**How does structure affect wind speed and wind flow?**• Density – determines degree of wind speed reduction (and length of protected zone)**Density**Upwind Downwind**How does structure affect wind speed and wind flow?**• Density – determines degree of wind speed reduction (and length of protected zone) • Height – along with density, determines length of protected zone, upwind and downwind**WIND**HEIGHT Protected Area 2-5 H 10-20 H Protected Area Protected Area**How does structure affect wind speed and wind flow?**• Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection**LENGTH**End effect: Windspeeds increased around end of windbreak by 1.1-1.3 times**PROTECTED AREA**Length:Height - > 10:1**How does structure affect wind speed and wind flow?**• Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection • Orientation – place perpendicular to prevailing winds**Wind**ORIENTATION**?**Wind**?**PROTECTED AREA Wind**Wind**PROTECTED AREA ? PROTECTED AREA**From Northerly or northwesterly Direction 12 out of 24**From Southeasterly or Easterly Direction 10 out of 24 From Southwesterly Direction 2 out of 24**How does structure affect wind speed and wind flow?**• Density – determines degree of wind speed reduction • Height – with density, determines length of protected zone, upwind and downwind • Length – determines total area of downwind protection • Orientation – place perpendicular to prevailing winds • Continuity